Method and apparatus for managing time in a satellite positioning system

ABSTRACT

A method, apparatus and system for time management in a position-location system is described. The method may include (i) obtaining, at a global-navigation-satellite-system receiver while being served by a first node of a wireless network a first time base, a relative-time difference, and a third time base; and forming a time relation as a function of the first time base, relative-time difference (“RTD”) and third time base. The first time base is associated with the first node, and may be, for example, a time base associated with an air interface for communicating with the first node. The RTD may be a difference between the first time base and a second time base associated with a second node of the wireless network. The third time base is associated with a constellation of satellites, and may be, for example, an absolute time associated with the constellation of satellites. The method may include using knowledge of a GNSS time to enhance sensitivity or time to first position of a GNSS receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 10/976,191, filed on Oct. 28, 2004, which claimsbenefit of U.S. Provisional Patent Application Ser. No. 60/518,180,filed Nov. 7, 2003, both of which are incorporated herein by referencein their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to satelliteposition location systems and, more particularly, to a method andapparatus for managing time in a Global-Navigation-Satellite System.

2. Description of the Related Art

Global-Navigation-Satellite-System (GNSS) receivers, such as GlobalPositioning System (GPS) receivers, use measurements from severalsatellites to compute position. GNSS receivers normally determine theirposition by computing time delays between transmission and reception ofsignals transmitted from satellites and received by the receiver on ornear the surface of the earth. The time delays multiplied by the speedof light provide the distance from the receiver to each of thesatellites that are in view of the receiver.

For example, each GPS signal available for commercial use utilizes adirect sequence spreading signal defined by a unique pseudo-random noise(PN) code (referred to as the coarse acquisition (C/A) code) having a1.023 MHz spread rate. Each PN code bi-phase modulates a 1575.42 MHzcarrier signal (referred to as the L1 carrier) and uniquely identifies aparticular satellite. The PN code sequence length is 1023 chips,corresponding to a one millisecond time period. One cycle of 1023 chipsis called a PN frame or epoch.

GPS receivers determine the time delays between transmission andreception of the signals by comparing time shifts between the receivedPN code signal sequence and internally generated PN signal sequences.These measured time delays are referred to as “sub-millisecondpseudoranges”, since they are known modulo the 1 millisecond PN frameboundaries. By resolving the integer number of milliseconds associatedwith each delay to each satellite, then one has true, unambiguous,pseudoranges. A set of four pseudoranges together with a knowledge ofabsolute times of transmission of the GPS signals and satellitepositions in relation to these absolute times is sufficient to solve forthe position of the GPS receiver. The absolute times of transmission (orreception) are needed in order to determine the positions of the GPSsatellites at the times of transmission and hence to compute theposition of the GPS receiver.

Accordingly, each of the GPS satellites broadcasts information regardingthe satellite orbit and clock data known as the satellite navigationmessage. The satellite navigation message is a 50 bit-per-second (bps)data stream that is modulo-2 added to the PN code with bit boundariesaligned with the beginning of a PN frame. There are exactly 20 PN framesper data bit period (20 milliseconds). The satellite navigation messageincludes ephemeris data, which identifies the satellites and theirorbits, as well as absolute time information (also referred to herein as“GPS time”, “satellite time”, or “time-of-day”) associated with thesatellite signals. The absolute time information is in the form of asecond of the week signal, referred to as time-of-week (TOW). Thisabsolute time signal allows the receiver to unambiguously determine atime tag for when each received signal was transmitted by eachsatellite.

In some GPS applications, the signal strengths of the satellite signalsare so low that either the received signals cannot be processed, or thetime required to process the signals is excessive. As such, to improvethe signal processing, a GPS receiver may receive assistance data from anetwork to assist in satellite signal acquisition and/or processing. Forexample, the GPS receiver may be integrated within a cellular telephoneand may receive the assistance data from a server using a wirelesscommunication network. This technique of providing assistance data to aremote mobile receiver has become known as “Assisted-GPS” or A-GPS.

In some A-GPS systems, the wireless communication network that providesthe assistance data is not synchronized to GPS time. Suchnon-synchronized networks include time division multiple access (TDMA)networks, such as GSM networks, universal mobile telecommunicationssystem (UMTS) networks, North American TDMA networks (e.g., IS-136), andpersonal digital cellular (PDC) networks.

In these types of networks, absolute time information is presentlyobtained at the base stations of such wireless networks using co-locatedlocation measurement units (LMUs). Each of these conventional LMUsincludes a GPS receiver that is used to receive and decode the TOWinformation from the satellites in view of the base stations that arenear the LMU. The conventional LMU then computes an offset between GPStime and the local time at such base stations. The offset is thensupplied to the base stations, which in turn, use the offset to correcttheir local time. One disadvantage associated with conventional LMUs isthat the wireless communication network typically includes manythousands of base stations, thus requiring many conventional LMUs.Providing a large number of conventional LMUs is significantlyexpensive, and is thus undesirable.

Therefore, there exists a need in the art for a method and apparatusthat manages time within an assisted GNSS without employing conventionalLMUs.

SUMMARY

A method, apparatus and system for time management in aposition-location system is described. The method may include obtaining,at a given global-navigation-satellite-system (“GNSS”) receiver whilebeing served by a first node of a wireless network (e.g., a first basestation), a first time base, a relative-time difference, and a thirdtime base; and forming a time relation as a function of the first timebase, the relative-time difference (“RTD”) and the third time base.

The first time base is associated with the first node, and may be, forexample, a time base associated with an air interface used forcommunicating with the first node. The RTD may be a difference betweenthe first time base and a second time base associated with a second node(e.g., a second and/or neighboring base station) of the wirelessnetwork. The RTD may be obtained from measurements provided by thewireless network during a handover from the first node to the secondnode. The RTD may be or be formed from, for example,Enhanced-Observed-Time-Difference (“EOTD”) measurements if the wirelessnetwork is embodied as a global system for mobile communications (“GSM”)or universal mobile telecommunications system (“UMTS”) network orObserved-Time-Difference-of-Arrival (“OTDA”) measurements if thewireless network is embodied as a wideband code division multiple access(CDMA) network.

The third time base is associated with a constellation of satellites.The third time base may be or be formed from, for example, an absolutetime associated with the constellation of satellites (“GNSS systemtime”). This GNSS system time may be obtained by decoding satellitesignals received from one or more satellites of the constellation.Alternatively, the third time base may be an estimate of the GNSS systemtime maintained by the given GNSS receiver.

The method may also include storing at the GNSS receiver the timerelation, whereby, the GNSS receiver is adapted to compute its position(“receiver position”) as a function of the time relation. In addition,the method may include providing the time relation from the GNSSreceiver to a database for subsequent distribution to a second GNSSreceiver.

The apparatus may include a receiver for the GNSS (“GNSS receiver”). TheGNSS receiver, in turn, may include memory adapted to store executableinstructions, and a processor operable to obtain from the memory theexecutable instructions and execute the executable instructions. Theexecutable instructions include executable instructions to (i) obtainthe first time base, the relative-time difference, and the third timebase while being served by a first node of a wireless network; and (ii)form a time relation as a function of the first time base, therelative-time difference and the third time base.

Accordingly, the GNSS receiver may compute the receiver position (e.g.,a geographic position) and/or an estimate of the error of its own clockwith respect to the GNSSS system time. The GNSS receiver can then easilyassociate the GNSS system time with, for example, the air interface timeof the first node.

Although the foregoing includes only one RTD, the method, apparatus andsystem may be extended to more than one RTD, in which the additionalRTDs represent a difference between the first time base and time basesfor other (e.g., neighboring) nodes of the wireless network. This way,the GNSS receiver and/or the database may extend the relationshipbetween the GNSS system time and the time bases of such other nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features are attained andcan be understood in detail, a more detailed description, which isbriefly summarized above, is described below with reference to theFigures illustrated in the appended drawings.

It is to be noted that the Figures in the appended drawings, like thedetailed description, are examples. And as such, the Figures and thedetailed description are not to be considered limiting, and otherequally effective examples are possible and likely. Furthermore, likereference numerals in the Figures indicate like elements: wherein:

FIG. 1 is a first block diagram depicting an example of a positionlocation system;

FIG. 2 is a second block diagram depicting an example of a remotereceiver of a position-location system;

FIG. 3 is a third block diagram depicting an example of a server of aposition-location system;

FIG. 4 is a first flow diagram depicting an example of a process formanaging time in a position-location system;

FIG. 5 is second flow diagram depicting an example of a process fordetermining a position of a remote receiver in a position-locationsystem;

FIG. 6 is a third flow diagram depicting another example of a processfor determining a position of a remote receiver in a position-locationsystem;

FIG. 7 is a fourth flow diagram depicting another example of a processfor determining a position of a remote receiver in a position-locationsystem;

FIG. 8 is a fifth flow diagram depicting another example of a processfor managing time in a position-location system; and

FIG. 9 is a sixth flow diagram depicting another example of a processfor determining a position of a remote receiver in a position-locationsystem.

DETAILED DESCRIPTION

A method and apparatus for managing time in aGlobal-Navigation-Satellite System (GNSS) is described. Those skilled inthe art will appreciate that the invention may be used with varioustypes of mobile or wireless devices that are “location-enabled,” such ascellular telephones, pagers, laptop computers, personal digitalassistants (PDAs), and like type wireless devices known in the art.Generally, a location-enabled mobile device is facilitated by includingin the device the capability of processing GNSS satellite signals.

A GNSS receiver, such as remote receiver 102A, 102B and 200 (below),acquires a satellite signal by searching a given search space, which maybe defined as some or all possible time delays associated with the timeof travel (“travel time”) of such satellite signal from a satellite. Thetravel time is proportional to a range (in distance) from the GNSSreceiver to the satellite. Precise knowledge of GNSS system time can beused by the GNSS receiver to reduce the search space of such delays, andhence, decrease the amount time for acquiring the satellite signal. Inaddition, if the search space is small (typically on the order of tensof microseconds), the satellite signal can be integrated to increasesensitivity of the GPS receiver.

A less precise knowledge of GNSS system time (e.g., few milliseconds)may be used to time stamp measurements for determining the range andcomputing the receiver position, and obviates the need for the GNSSreceiver to demodulate or otherwise decode the GNSS system time from thesatellite signal. Obviating the need to demodulate or otherwise decodethe GNSS system time, decreases the amount of time the GNSS receiveremploys before a first receiver position is computed and/or delivered toa user of the GNSS receiver.

FIG. 1 is a block diagram depicting an example of a position-locationsystem 100, such as a Global Navigation Satellite System (GNSS). Thesystem 100 illustratively comprises remote receivers 102A and 102B(collectively referred to as remote receivers 102) in communication witha server 104 via a wireless communication network 106 (e.g., a cellulartelephone network). The server 104 may be disposed in a serving mobilelocation center (SMLC) of the wireless communication network 106.

The remote receivers 102 obtain satellite measurement data with respectto a plurality of satellites 110 (e.g., pseudoranges, Dopplermeasurements). The server 104 obtains satellite navigation data for thesatellites 110 (e.g., orbit trajectory information, such as ephemeris).Position information for the remote receivers 102 is computed using thesatellite measurement data and the satellite navigation data.

The wireless communication network 106 typically comprises anon-synchronized communication network (i.e., the network is notsynchronized with satellite time). The wireless communication network106 includes a plurality of nodes or base stations; two of which areillustratively shown as a first base station 108-1, which has a firstservice area 112-1, and a second base station 108-2, which has a secondservice area 112-2. The base stations 108-1, 108-2 of the wirelesscommunication network 106 may also be referred to herein as “cellsites”.

For purposes of clarity by example, the wireless communication network106 is shown as including only two service areas. It is to beunderstood, however, that the wireless communication network 106 mayinclude any number of service areas that serve any number of remotereceivers; each of which may operate and/or be located in the same or adifferent one of the service areas. Each of these remote receivers mayfunction as either the remote receiver 102A or the remote receiver 102B.In addition, the remote receiver 102A may function as the remotereceiver 102B, and the remote receiver 102B may function as the remotereceiver 102A.

The remote receiver 102A is illustratively shown as being within thefirst service area 112-1, in which wireless links 116-1 may beestablished between the remote receiver 102A and the base station 108-1.The remote receiver 102A may be adapted to register with the basestation 108-1 via the wireless links 116-1.

Communication between the base station 108-1 and the remote receiver102A may be facilitated via a wireless signal having a first time basethat is associated with the first base station 108-1. This first timebase may be, include or be formed from a particular timing structureassociated with an air interface of the wireless network (“air-interfacetiming”).

In one embodiment, the wireless communication network 106 may comprise aglobal system for mobile communications (GSM) network. For a basestation in a GSM network, the air-interface timing of a wireless signalis defined by a frame number, a timeslot number, and a bit number. Aframe has a duration of 4.615 milliseconds, a timeslot has a duration of577 microseconds, and a bit has a duration of 3.69 microseconds. A GSMbase station includes clock for managing its air-interface timing in asynchronous manner. The clock used by the GSM base station is a highlycontrolled and exhibits a low long term drift rate. Frequency offseterrors are usually less than 0.05 parts per million (ppm), and long termdrift rates are even lower. The GSM base stations and the air-interfacetiming of their communications are well known in the art.

Various other types of non-synchronized wireless networks exhibitair-interface timing structures similar to GSM, including, but notlimited to, universal mobile telecommunications system (UMTS) networks,North American time division multiple access (TDMA) networks (e.g.,IS-136), and personal digital cellular (PDC) networks. For purposes ofclarity by example, various aspects of the invention are described withrespect to GSM. It is to be understood, however, that the presentinvention may be used with other types of wireless networks, such ascode division multiple access (CDMA), wideband CDMA, UMTS, TDMA, PDC andlike networks.

Although the remote receiver 102A is shown as being within the firstservice area 112-1, the remote receiver 102A may be able to detectsignals, such emanating from the second base station 108-2. This mayoccur, for instance, by the remote receiver 102A moving into the secondservice area 112-2 and establishing wireless links 116-2 or, simply, bybeing in a location in the first service area 112-1 where attenuation ofthe signals emanating from the second base station 108-2 is limited sothat the remote receiver 102A can detect such signals. Communicationbetween the base station 108-2 and the remote receiver 102A may befacilitated via another wireless signal having a second time base thatis associated with the second base station 108-2. The second time basemay be, include or be formed from the air-interface timing that isassociated with the second base station 108-2.

In addition to above, the remote receiver 102A, when registered with orotherwise served by the first base station 108-1, may be adapted tomeasure or otherwise obtain (i) one or more power levels associated withthe first and/or second base stations 108-1, 108-2, and/or (ii) one ormore time differences between the first time base (“serving-time base”)and the second time base (“neighbor-time base”). The remote receiver102A may be further adapted to form a relative-time difference (RTD) asa function of the serving-time base and the neighbor-time base.

The remote receiver 102A may also be adapted to provide or “up link” tothe wireless network 106 the RTD, the serving-time base and/or theneighbor-time base for handover purposes. In addition, the remotereceiver 102A may be adapted to provide to the server 104 the RTD, theserving-time base and/or the neighbor-time base.

The remote receiver 102B is illustratively shown as being within thesecond service area 112-2, in which wireless links 116-2 may beestablished between the remote receiver 102B and the base station 108-2.The remote receiver 102B may be adapted to register with the basestation 108-2 via the wireless links 116-2. Communication between thebase station 108-2 and the remote receiver 102B may be facilitated viathe wireless signal having the second time base.

Satellite navigation data, such as ephemeris for at least the satellites110, may be collected by a network of tracking stations (“referencenetwork 114”). The reference network 114 may include several trackingstations that collect satellite navigation data from all the satellitesin the constellation, or a few tracking stations, or a single trackingstation that only collects satellite navigation data for a particularregion of the world. An exemplary system for collecting and distributingephemeris is described in commonly-assigned U.S. Pat. No. 6,411,892,issued Jun. 25, 2002, which is incorporated by reference herein in itsentirety. The reference network 114 may provide the collected satellitenavigation data to the server 104.

The remote receivers 102 may be configured to receive assistance datafrom the server 104 via the wireless network 106. For example, theremote receivers 102 may receive acquisition assistance data, satellitetrajectory data, or both from the server 104.

Acquisition assistance data (i.e., data configured to assist the remotereceiver 102 in detecting and processing satellite signals from thesatellites 110) may be computed by the server 104 using satellitetrajectory data (e.g., ephemeris or other satellite trajectory model).For example, the acquisition assistance data may include expectedpseudoranges (or code phases) from the satellites 110 to an assumed(e.g., an approximate) position of a respective one of the remotereceivers 102 at an assumed time-of-day, and/or a model of expectedpseudoranges (e.g., pseudorange model). Exemplary processes for formingpseudorange models as acquisition assistance data are described incommonly-assigned U.S. Pat. No. 6,453,237, issued Sep. 17, 2002, whichis incorporated by reference herein in its entirety.

Satellite trajectory assistance data may include ephemeris, Almanac, orsome other orbit model. Notably, the satellite trajectory data maycomprise a long term satellite trajectory model, as described incommonly-assigned U.S. Pat. No. 6,560,534, issued May 6, 2003, which isincorporated by reference herein in its entirety.

The position-location system 100 may be configured in multiple modes ofoperation. In one embodiment, the remote receivers 102 obtain satellitemeasurements (e.g., pseudoranges) and send the satellite measurements tothe server 104 through the wireless network 106, where the server 104computes a position of the remote receivers 102 (referred to as a mobilestation assisted or “MS-Assisted” configuration).

In another embodiment, the remote receivers 102 obtain satellitetrajectory data from the server 104, and obtain the satellitemeasurements (e.g., pseudoranges) from the satellites 110. The remotereceivers 102 use the satellite measurements and the satellitetrajectory data to locate their own position (referred to as a mobilestation based or “MS-Based” configuration).

In yet another embodiment, the remote receivers 102 may obtain satellitetrajectory data directly from the satellites 110 and locate their ownposition (referred to as the “autonomous” configuration). Furthermore,the remote receiver 102A may operate in a different mode than the remotereceiver 102B. Regardless of the configuration employed (i.e.,MS-assisted, MS-based, or autonomous), the position-location system 100may employ various embodiments for managing time, as described below, toobtain a sufficiently accurate estimate of satellite time, which is alsocommonly referred to as “absolute time”.

FIG. 2 is a block diagram depicting an example of a remote receiver 200of a position-location system, such as receiver for a GNSS. The remotereceiver 200 may be used as either or both of the remote receivers 102of FIG. 1.

The remote receiver 200 illustratively comprises a satellite signalreceiver 204, a wireless transceiver 206, a processor 202, a memory 208,and clock circuitry 210. The satellite signal receiver 204 receivessatellite signals from the satellites 110 using an antenna 212. Thesatellite signal receiver 204 may comprise a conventional A-GPSreceiver. An exemplary A-GPS receiver is described in U.S. Pat. No.6,453,237, referenced above.

The wireless transceiver 206 receives wireless signals from the basestations 108-1, 108-2 of the wireless communication network 106 via anantenna 214. The satellite signal receiver 204 and the wirelesstransceiver 206 may be controlled by the processor 202.

The processor 202 may comprise a microprocessor, instruction-setprocessor (e.g., a microcontroller), or like type processing elementknown in the art. The processor 202 is coupled to the memory 208 and theclock circuitry 210. The memory 208 may be random access memory, readonly memory, removable storage, hard disc storage, or any combination ofsuch memory devices. The memory 208 may be adapted to store the RTD, theserving-time relation and/or the neighbor-time relation.

Various processes and methods described herein may be implemented viasoftware, such as (i) time-relation-forming software 216 for performingsome or all of a time-relations-forming process (e.g., a processillustratively set forth in FIG. 4), (ii) managing-time software 218 forperforming some or all of a managing-time process (e.g., processillustratively set forth in FIG. 8), (ii) position-determining software220 for performing some or all of a position-determining process (e.g.,processes illustratively set forth in FIGS. 5, 6, 7 and 9). Thissoftware 216-220 may be stored in the memory 208 for execution by theprocessor 202. Alternatively, such processes and methods may beimplemented using dedicated hardware, such as an application specificintegrated circuit (ASIC), or a combination of hardware and software.The clock circuitry 210 may include one or more well known clockdevices, such as a real-time clock (RTC), oscillators, counters, and thelike.

FIG. 3 is a block diagram depicting an example of a server 104 of theposition-location system, such as the system 100 shown in FIG. 1. Theserver 104 illustratively comprises an I/O interface 302, a centralprocessing unit (CPU) 304, support circuits 306, and a memory 308. TheCPU 304 is coupled to the memory 308 and the support circuits 306. Thememory 308 may be random access memory, read only memory, removablestorage, hard disc storage, or any combination of such memory devices.The support circuits 306 include conventional cache, power supplies,clock circuits, data registers, I/O interfaces, and the like tofacilitate operation of the server 104. The I/O interface 302 isconfigured to receive satellite navigation data from the referencenetwork 114. The I/O interface 302 is also configured for communicationwith the wireless communication network 106.

Various processes and methods described herein may be implemented usingsoftware, such as (i) time-relation-forming software 316 for performingsome or all of a time-relations-forming process (e.g., processillustratively set forth in FIG. 4), (ii) managing-time software 318 forperforming some or all of a managing-time process (e.g., processesillustratively set forth in FIG. 8), (ii) position-determining software320 for performing some or all of a position-determining process (e.g.,processes illustratively set forth in FIGS. 5, 6 and 9). This software316-320 may be stored in the memory 308 for execution by the CPU 304.Alternatively, the server 104 may implement such processes and methodsin hardware or a combination of software and hardware, including anynumber of processors independently executing various programs anddedicated hardware, such as application specific integrated circuits(ASICs), field programmable gate arrays (FPGAs), and the like.

FIG. 4 is a flow diagram depicting an example of a process for formingtime relations (time-relation-forming process) 400 in aposition-location system, such as a GNSS. The time-relation-formingprocess 400 may be understood with simultaneous reference to theposition-location system 100 of FIG. 1. For purposes of clarity byexample, the time-relation-forming process 400 is described with respectto the remote receiver 102A. The process 400 may also be performed bythe remote receiver 102B.

The time-relation-forming process 400 begins at process block 402, whereGNSS system time is derived or otherwise determined at the remotereceiver 102A in the service area 112-1 of the base station 108-1. Inone embodiment, the remote receiver 102A may determine GNSS system timeby processing satellite signals from the satellites 110 to decode atime-of-week (TOW) value, which may be used to determine GPS time. Theprocess of decoding satellite signals to obtain the TOW value is wellknown in the art.

In another embodiment, the remote receiver 102A may compute the GNSSsystem time using a “time-free” navigation solution. Notably, the remotereceiver 102A may use a position estimate, a time estimate, andsatellite trajectory data along with satellite measurements in amathematical model to compute absolute time. An exemplary “time-free”navigation solution is described in commonly-assigned U.S. Pat. No.6,734,821, issued May 11, 2004, which is incorporated by referenceherein in its entirety.

At process block 404, the remote receiver 102A obtains the RTD. Tofacilitate this, the mobile receiver 102A may measure the serving-timebase and neighbor-time base. The serving-time base and neighbor-timebase may be, include or be formed from, for example, the first andsecond air-interface timing from the first and second base stations108-1, 108-2, respectively. The remote receiver 102A may obtain thefirst and second air-interface times by monitoring, storing, and/orderiving from the wireless signals (e.g., from GSM frames in a GSMnetwork) broadcast or otherwise transmitted from the first and secondbase stations 108-1, 108-2, respectively.

The remote receiver 102A may obtain the first and second interface timesfrom both the first and second base stations 108-1, 108-2 when operatingin the first serving area 112-1. For example, the remote receiver 102Amay obtain the first and second air-interface times by synchronizing tothe respective first and second air-interface timing of the first andsecond base stations 108-1, 108-2 while operating in the first servingarea 112-1, and then deriving the first and second air-interface timestherefrom.

Alternatively, the remote receiver 102A may obtain the first and secondair-interface times by synchronizing to the first air-interface timingof the first base station 108-1, and (ii) detecting the secondair-interface timing of the second base station 108-2 while operating inthe first serving area 112-1. Thereafter, the remote receiver 102A mayderive the first air-interface time from signals used to synchronize theremote receiver 102A to the first base station 108-1, and derive thesecond air-interface time from the signals emanating from the secondbase station 108-2 and detected by the remote receiver 102A.

As another alternative, the remote receiver 102A may obtain the firstand second interface times from the first and second base stations108-1, 108-2, respectively, after operating in the both of the first andsecond serving areas 112-1, 112-2. For example, the remote receiver 102Amay obtain the first and second air-interface times by (i) synchronizingto the second air-interface timing of the second base station 108-2while operating in the second serving area 112-2, and then after movinginto the first serving area 112-1, (ii) synchronizing to the firstair-interface timing of the first base station 108-1. Thereafter, thefirst and second air-interface times are derived as described above.

The remote receiver 102A may store the RTD, the serving-time base andneighbor-time base along with a reference to the first base station108-1 and/or the second base station 108-2. After process block 404, thetime-relation-forming process 400 transition to process block 406.

At process block 406, a time relation is formed as a function of theRTD, serving-time base and the GNSS system time. In one embodiment, thetime relation may be established between TOW values and frame numbers ofthe wireless signals transmitted by the base stations 108-1, 108-2. Inanother embodiment, the time relation may be a time offset computedbetween each of the first and second air-interface times and thesatellite time, respectively. In another embodiment, the time relationis formed between frame timing of the base station 108-1, TOW and theRTD Other relationships between the first and second air-interface timesand satellite time may be formed as well. As another alternative, thetime relation may be formed by applying the first time base to the RTDto determine the second time base; and forming the time relation as afunction of the second and the GNSS system time.

At process block 408, the time relation are optionally compensated forpropagation delay between the remote receiver 102A and the base station108-1 (given the remote receiver 102A is operating in serving area112-1) so as to form a compensated time relation before storing inmemory 208 (process block 410) and/or propagating the compensated timerelation to the server 104 (process block 412). In one embodiment, theremote receiver 102A forms the compensated time relation by appending atiming advance value to each of the first and second time bases. Inaddition to or in lieu of the propagation delay between the base station108-1 and the remote receiver 102A, the base station 108-1 may append atiming advance value, such as described below, to the compensated (oruncompensated) time relation.

Notably, TDMA communication systems compensate for the effect ofpropagation delay by synchronizing the arrival of transmissions fromvariously located mobile receivers (such as the remote receivers 102) toslotted frame structures used by base stations (such as the first andsecond base stations 108-1, 108-2). To synchronize transmissions fromthe mobile receivers located in a service area of a serving basestation, the serving base station typically transmits a timing advance(TA) value to each of the mobile receivers. Responsively, such mobilereceivers advance their transmissions to the serving base stationaccording to the TA values to compensate for the propagation delaybetween the mobile receiver and the serving base station. Typically, theTA values cause the mobile receivers to advance their uplinktransmissions (i.e., transmissions to the serving base station) suchthat these uplink transmissions from the mobile receivers served by theserving base station arrive at the serving base station in synchronismwith a common receive frame structure. Such a timing advance techniqueis well known in the art. Other air interfaces such as WCMDA in UMTS usea similar quantity referred to as Round Trip Timing (RTT).

At process block 410, the compensated or uncompensated time relation isstored locally in memory 208 for later use by the remote receiver 102A.The remote receiver 102A, for example, may use the compensated (oruncompensated) time relation for acquiring one or more of the satellites110, computing its position, and other functions involving the satellitesignals. As described in more detail below, the time relation for thefirst and second base stations 108-1, 108-2 may be used in aposition-location process of the remote receivers 102A, 102B when beingserved in any of the service areas 112-1, 112-2.

Alternatively, the remote receiver 102A may derive and store in itsmemory 208 a second time relation or a time-relation model (e.g., amathematical equation) as a function the compensated (or uncompensated)time relation. This second time relation or time-relation model may, forexample, relate the compensated (or uncompensated) time relation toanother compensated (or uncompensated) time relation. In addition, thesecond time relation and/or the time-relation model may be stored in thememory 208 in lieu of the compensated (or uncompensated) time relation.This beneficially preserves an amount of free space of the memory 208otherwise used to store each of the time relations.

For simplicity, the first and any other time relations, whethercompensated or uncompensated, may be referred to hereinafter withoutdenoting whether they are compensated or uncompensated. These timerelations, however, may be either compensated or uncompensated.Similarly, the time-relation model may be formed with and/or formcompensated or uncompensated time relations, even though notspecifically noted.

In addition, the first and any other time relations and/or thetime-relation model may be stored along with designations associatedwith the respective coverage areas of the cell sites. These designationsmay be, for example, identifiers or other emanated signal signaturesassociated to the first and second base stations 108-1, 108-2. Theidentifiers may be, for example, cellular identifications (cell-IDs)assigned to or otherwise given to the first and second base stations108-1, 108-2.

Like above, the remote receiver 102A may derive and store in its memory208 a relational-designation model (e.g., a mathematical equation) as afunction the designations. The relational-designation model may, forexample, relate each of the designations to beneficially preserve anamount of free space of the memory 208 otherwise used to store each ofthe designations.

Alternatively and/or additionally, the remote receiver 102A maypropagate the first and any other time relations and/or thetime-relation model to the server 104 for storage and later retrieval,as shown in process block 412. In one embodiment, the first and othertime relations and/or the time-relation model are sent to the server 104using a GPS measurement information element defined in ETSI TS 101 527,version 7.15.0 (also known as 3GPP TS 04.31 and referred to herein as TS4.31), which is incorporated by reference herein in its entirety.

Notably, TS 4.31 defines a GPS measurement information element fortransmitting satellite measurements from the remote receiver 102A to theserver 104 in an MS-assisted configuration. As shown in Table A.5 of TS4.31 (reproduced below), the GPS measurement information elementincludes fields from reference frame, GPS TOW, the number of satellitesto which measurements have been made, and the satellite measurementinformation. The presence column relates to whether the field ismandatory (M) or optional (O). The occurrences column relates to thenumber of times the given field is present in the information element.

TABLE A.5 Element fields Presence Occurrences Reference Frame O 1 GPSTOW M 1 # of Satellites (N_SAT) M 1 Measurement Parameters M N_SAT

The first and other time relations and/or the time-relation model may besent to the server 104 using (i) the GPS TOW field for providing the TOWvalue obtained at process block 402, and (ii) the Reference Frame fieldfor providing the frame number associated with the TOW value at processblock 404. At process block 414, the first and other time relationsand/or the time-relation model may be stored in the memory 308 of theserver 104. The first and other time relations and/or the time-relationmodel may be stored along with the designations associated with therespective coverage areas of the cell sites.

The server 104 may obtain the designations for the cell sites from theremote receiver 102A when the remote receiver 102A sends the first andother time relations and/or the time-relation model to the server 104.The time of sending, however, in not determinative. That is, thedesignations may be sent along with or separate from, but associatedwith the first and other time relations and/or the time-relation model.

Alternatively, the server 104 may obtain the designations for the cellsites from the cell sites themselves. For example, the server 104 mayinspect a call routing scheme of communications between the server 104and the remote receiver 102A to determine which of the first and secondbase stations 108-1, 108-2 is serving the remote receiver 102A, andusing this information the server 104 can determine (e.g., extract) thedesignation.

The time-relation-forming process 400 may be repeated with respect tovarious base stations in the wireless communication network 106 suchthat the remote receiver 102A and/or the server 104 accumulates, updatesand/or maintains a collection of time relations and/or one or moretime-relation models associated with these various base stations.

Using the collection of time relations and/or one or more time-relationmodels locally stored in memory 208 and/or obtaining from the server 104the collection of time relations and/or one or more time-relation modelsobviates the need for the remote receiver 102A to determine thesatellite time from the satellite signals. In this manner, a singleremote receiver, such as the remote receiver 102A, may perform thefunctions of a conventional LMU for all of the remote receivers incommunication with the first and second base station 108-1, 108-2,including, for example, the remote receiver 102B. In turn, this obviatesthe need for the conventional LMU within the vicinity of the basestations 108-1, 108-2.

FIG. 5 is flow diagram depicting an example of a process 500 fordetermining a position of a remote receiver of a position-locationsystem, such as a GNSS. This process for determining the position of theremote receiver (hereinafter position-determining process 500) may bedeployed using a MS-Assisted or MS-Based configuration. In addition, theposition-determining process 500 may be understood with simultaneousreference to the position-location system 100 of FIG. 1.

For purposes of clarity by example, the position-determining process 500is described with respect to the remote receiver 102B. Theposition-determining process 500 may also be performed by the remotereceiver 102A.

The position-determining process 500 begins at process block 502, wheresatellite measurements are obtained at the remote receiver 102B whileoperating (e.g., being served) in the second service area 112-2. Thesesatellite measurements may be pseudoranges to a plurality of satellitesusing satellite positioning system signals. The process of measuringpseudoranges using satellite positioning system signals is well known inthe art.

At process block 504, the satellite measurements are time-stamped usingthe second time base . The first time base may be the air-interfacetiming of the second base station 108-2. At process block 506, thetime-stamped measurements are sent to the server 104.

At process block 508, the first time relation, which corresponds to thebase station 108-2, is obtained from memory 308 of the server 104. Asdescribed above, the server 104 may be configured to store a collectionof time relations or time-relation models for the base stations of thewireless communication network 106, including the first and second basestations 108-1, 108-2. These time relations may comprise associationsbetween RTD, GNSS system time, and the first time base.

At process block 510, corrected time-stamped measurements are formedusing the first time relation. For example, the server 104 may form thecorrected time-stamped measurements by using the first time relation toconvert a value of the time-stamped measurements as a function of theRTD and GNSS system time.

At process block 512, a position of the remote receiver 102B is computedusing the corrected time-stamped measurements. The position computationprocess is well known in the art.

Although the position-determining process 500 is deployed in anMS-Assisted configuration, the position of the mobile receiver 102 maybe determined, as described below, using a like-kindposition-determining process and a MS-Based configuration.

Notably, FIG. 6 is a flow diagram depicting another example of a process600 for determining a position of a remote receiver of aposition-location system, such a GNSS receiver. This process fordetermining the position of the remote receiver (hereinafterposition-determining process 600) may be deployed using a MS-Basedconfiguration. In addition, the position-determining process 600 may beunderstood with simultaneous reference to the position-location system100 of FIG. 1.

For purposes of clarity by example, the position-determining process 600is described with respect to the remote receiver 102B. Theposition-determining process 600 may also be performed by the remotereceiver 102A.

The position-determining process 600 begins at process block 602, wherethe remote receiver 102B obtains the first time base (e.g., the firstair-interface timing of the first base station 108-1) while operating inthe second serving area 112-2 and being served by the second basestation 108-2. At process block 604, the remote receiver 102B sends tothe server 104 a request for the first time relation. As an alternative,the remote receiver 102B sends to the server 104 a request for thefirst, second and/or other time relations and/or the time-relationmodel. The request may be included in a request for assistance data.

Responsive to the request, the remote receiver 102B, at process block606, obtains from the server 104 the first time relation and thecorresponding designations for the first and second base stations108-1,108-2. Alternatively, the remote receiver 102B may obtain from theserver 104 the first, second and/or other time relations and/or thetime-relation model; and the designations for the first and second basestations 108-1, 108-2 (and/or various other base stations) Forsimplicity, however, the following exposition references only the firsttime relation, and a designations that corresponds to the first basestation 108-1 (first designation).

The first time relation and the first designations may be sent from theserver 104 to the remote receiver 102B using, for example, a GPSassistance data element defined in TS 4.31. Notably, the TS 4.31 definesa GPS assistance data element for providing assistance data to theremote receiver 102B in both an MS-Assisted and an MS-Basedconfiguration.

As shown in Table A.14 of TS 4.31, the GPS assistance data elementincludes (i) a GPS TOW field for providing a TOW value, and (ii) a framenumber, a time slot number and a bit number field for providing the airinterface time of the serving base station associated with the TOWvalue. The remote receiver 102B may use the GPS TOW and the frame fieldsto obtain knowledge of the GPS time with very high precision (fewmicroseconds) despite the latency of the wireless link and thus improvethe positioning performance of the remote receiver 102B. It is wellknown in the art that a priori knowledge of GNSS system time with highprecision helps GNSS receivers with the acquisition of satellite signalsand the accuracy of the resulting receiver position.

At process block 606, the remote receiver 102B obtains satellitemeasurements from one or more of the satellites 110. These satellitemeasurements may be, for example, pseudoranges to a plurality ofsatellites. At process block 608, position of the remote receiver 102Bis computed using the satellite measurements, the first and second timerelations, and the first time base.

To facilitate the computing the position of the remote receiver 102B,the satellite measurements may be time stamped using clock circuitrysynchronized to the second time base (e.g., the air-interface timing ofthe second base station 108-2) because the remote receiver 102B isoperating in the second service area 112-2. Assuming that the timerelation is formed as a function of the RTD and the GNSS system time,the time relation may be used to convert the time stamps so as toprovide the GNSS system time relative to the second time base. The timerelation may then be used to provide the GNSS system time.

Alternatively, the satellite measurements may be time stamped usingclock circuitry that has been adjusted to track the first time base.Assuming that the time relation is formed relative as a function of theRTD and the GNSS system time, the time relation may be used to convertthe time stamps to provide the GNSS system time. In such case, thesecond time base need not be used.

The position-determining process 600 beneficially allows the remotereceiver 102B to determine satellite time using the first and/or othertime relations and/or the time-relation model. This way, if the remotereceiver 102B is able to obtain time base for any of the cell sites (andnot necessarily a cell site serving the remote receiver 102B) it candetermine the precise satellite time using the corresponding timerelation.

Moreover, the remote receiver 102B can store the time relation andcorresponding designation for later use with other cell sites fordetermining the precise satellite time. This way, the remote receiver102B can operate autonomously until it moves to a cell site for which itdoes not have a corresponding time relation or unless one of the timerelations for a cell site becomes obsolete due to changes, updates orrevisions to the air-interface timing of one or more of the cell sites.

Referring now to FIG. 7, a flow diagram depicting another example of aprocess 700 for determining a position of a remote receiver of aposition-location system, such a GNSS receiver, is shown. This process700 for determining the position of the remote receiver (hereinafterposition-determining process 700) may be deployed using an autonomousconfiguration. In addition, the position-determining process 700 may beunderstood with simultaneous reference to the position-location system100 of FIG. 1.

For purposes of clarity by example, the position-determining process 700is described with respect to the remote receiver 102B. Theposition-determining process 700 may also be performed by the remotereceiver 102A.

The position-determining process 700 begins at process block 702, wherethe remote receiver 102B obtains the first time base while operating inthe second serving area 112-2 and being served by the second basestation 108-2. At process block 704, the remote receiver 102B obtainsfrom its memory 208 the first and second time relations, which may havebeen formed via the time-relation-forming process 400 (FIG. 4) or othertime relation forming process.

As an alternative, the remote receiver 102B may obtain from its memory208 another time relation and/or the time-relation model in addition toor instead of the first and second time relations. To facilitateobtaining the first, second and/or other time relations and/or thetime-relation model, the remote receiver 102B may use the correspondingdesignations for the first and second base stations 108-1, 108-2 (and/orvarious other base stations)

At process block 706, the remote receiver 102B obtains satellitemeasurements from one or more of the satellites 110. These satellitemeasurements may be, for example, pseudoranges to a plurality ofsatellites. At process block 708, position of the remote receiver 102Bis computed using the satellite measurements; the air-interface timingof the first base station 108-1; and/or the first, second and/or thirdtime relations and/or the time-relation model.

To facilitate the computing the position of the remote receiver 102B,the satellite measurements may be time stamped using clock circuitrysynchronized to the second time base because the remote receiver 102B isoperating in the second service area 112-2. Assuming that the timerelation is formed as a function of the RTD, GNSS system time and thefirst time base, the time relation may be used to convert the timestamps so as to provide the GNSS system time relative to the second timebase. The time relation may then be used to provide the GNSS systemtime.

Alternatively, the satellite measurements may be time stamped usingclock circuitry that has been adjusted to track the first time base.Assuming that the time relation is formed as a function of the RTD, GNSSsystem time and the first time base, the time relation may be used toconvert the time stamps to provide the GNSS system time. In such case,the second time base need not be used.

The position-determining process 700 beneficially allows the remotereceiver 102B to determine satellite time using the first and/or othertime relations and/or the time-relation model. As above, if the remotereceiver 102B is able to obtain the time bases for any of the cell sites(and not necessarily a cell site serving the remote receiver 102B) itcan determine, using the corresponding time relations, the precise GNSSsystem time.

Because the remote receiver 102B stores and/or maintains the timerelations and corresponding designations for later use with other cellsites, it can determine the precise satellite time when operating in anycell site for which it possesses a corresponding time relation. Thisway, the remote receiver 102B can operate autonomously until it moves toa cell site for which it does not have a corresponding time relation orunless one of the time relations for a cell site becomes obsolete due tochanges, updates or revisions to the air-interface timing of one or moreof the cell sites. In such case, the remote receiver 102B can performthe time-relation-forming process 400 (FIG. 4) or other time relationforming process.

In another embodiment, time is managed by storing at the remote receiver102B time offsets between GNSS system time and the time bases of basestations within the wireless communication network 106. The presentembodiment may be used regardless of the configuration of theposition-location system 100 (e.g., MS-Assisted, MS-Based, autonomous)and may be used to determine precise time-of-day. For example, in thepresent embodiment, satellite time may be determined to within 100microseconds.

In particular, FIG. 8 is a flow diagram depicting another example of aprocess for managing time (managing-time process) 800 in aposition-location system, such as a GNSS. This managing-time process 800may be understood with simultaneous reference to the position-locationsystem 100 of FIG. 1. For purposes of clarity by example, themanaging-time process 700 is described with respect to the remotereceiver 102A. The managing-time process 800 may also be performed bythe remote receiver 102B.

The managing-time process 800 begins at process block 802, wheresatellite time is obtained at the remote receiver 102A in the servicearea 112-1 of the base station 108-1. Hitherto, the remote receiver 102Ahas no knowledge of precise satellite time. The remote receiver 102Amay, for example, determine satellite time by processing satellitesignals from the satellites 110 to decode a TOW value, which in turn,may be used to determine GNSS system time. In another embodiment, theremote receiver 102A may compute satellite time using a “time-free”navigation solution using for example, the time free process notedabove.

At process block 804, the derived satellite time is related to the firsttime base to produce a first time offset. For example, the first timeoffset may be formed as a function of the frame timing of the signalsemanating from the base station 108-1 and GNSS system time. Given that aclock of the base station 108-1 is highly accurate and frame timing issynchronous, accuracy of the first time offset is maintained.

At process block 806, the first time offset is stored within the memory208 of remote receiver 102A. The first time offset stored in the remotereceiver 102A typically occupies very little amount of memory (e.g., 8to 20 bytes).

Once the first time offset is stored in memory, the remote receiver 102Amay go to sleep, be turned off, or otherwise be deactivated. When theremote receiver 102A is re-activated and detects signals from the firstbase station 108-1 that match the first time offset, the remote receiver102A may establish precise satellite time using the first time offset.The clock circuitry of the remote receiver 102A may include a real timeclock to resolve any network rollover ambiguities.

When the remote receiver 102A is handed off from the first base station108-1 to the second base station 108-2, a second time offset may be usedto overcome the timing relationship that could otherwise be lost innetworks that do not synchronize each of the base stations to a commontiming (e.g., GSM). Thus, at process block 808, the remote receiver 102Amonitors for handovers. Optionally, the remote receiver 102A may modelthe drift of the clock of the first base station 108-1 (and/or otherbase station). Notably, the remote receiver 102A may make an accurateestimate of the long term drift rate of the base station clock as longas the remote receiver 102A remains in the service area of the firstbase station. In this manner, the remote receiver 102A may improve thetime offset stored for the base station 108-1 (and/or other basestation).

At process block 810, a determination is made as to whether the remotereceiver 102A has been instructed to hand over to the second basestation 108-2. If not, the managing-time process 800 returns to processblock 808. If so, the managing-time process 700 proceeds to processblock 812.

At process block 812, the first time offset for the first base station108-1 (or other time relation between the GNSS system time, the firsttime. base and the second time base) is extracted and used to tracksatellite time in the remote receiver 102A. For example, the remotereceiver 102A may use the first time offset to transfer the GNSS systemtime to counter circuitry during the handover.

At process block 814, the remote receiver 102A synchronizes to thesecond time base after the handover. Using the first time offset, theremote receiver 102A continues to track satellite time. At process block816, the GNSS system time is related to the second time base toestablish a second time offset for the second base station 108-2.

The time-managing process 800 may then return to process block 806 tostore in memory the second time offset, and/or the RTD. In this manner,the remote receiver 102A may store and maintain a collection of timeoffsets for a number of base stations, including the first and secondbase stations 108-1, 108-2, in the wireless communication network 106.

Because the first and second time bases are obtained every time theremote receiver 102A synchronizes to the one of the base stations 108-1,108-2, respectively, which has to (and typically) occurs each time theremote receiver 102A needs to communicate with communication network106, the remote receiver 102A does not have to transmit signals toobtain this time relationship. Consequently, no power is consumed duringidle states. In addition, the remote receiver 102A can be totallypowered down, restarted, and thereafter obtain precise satellite timefor any cell site for which it has or can obtain a corresponding one ofthe time relations without obtaining the precise satellite time from anexternal source. Thus, the present invention saves power, whilepreserving precise satellite time. In addition, network frame countersare synchronous and stationary. Any Doppler shift caused by movingeffects would be removed.

Many cellular telephones that have integrated A-GPS receivers includehardware for performing timing comparisons. Thus, the managing-timeprocess 800 may be used to provide time management traditionallyprovided by conventional LMUs. This managing-time process 800 supplantsobtaining precise satellite time from an external source with measuringtime locally within the remote receiver 102A. As such, the remotereceiver 102A obviates the need for providing a conventional LMU withinthe vicinity of the base stations 108-1,108-2.

FIG. 9 is a flow diagram depicting another example of a process fordetermining position of a remote receiver (position-determining process)900 in a position-location system, such as a GNSS. Theposition-determining process 900 may be understood with simultaneousreference to the position-location system 100 of FIG. 1. For purposes ofclarity by example, the position-determining process 900 s describedwith respect to the remote receiver 102A. The position-determiningprocess 900 may also be performed by the remote receiver 102B.

The position-determining process 900 begins at process block 902, wherethe remote receiver 102A synchronizes to the first time base, and thus,obtains the designation of the cell site (i.e., the first designation).At process block 904, the remote receiver obtains from its memory 208the time relation or time offset for the base station 108-1, whichcorresponds to the first designation.

As described above, the remote receiver 102A may be configured to storea collection of time offsets, where each of the time offsets comprisesan offset between the air-interface timing of its respective basestation and satellite time. Alternatively and/or additionally, theremote receiver 102A may be configured to store a collection of timerelations formed as a function of the GNSS system time and the timebases of at least two base stations. Each of these time relations, forexample, may have a given relationship to (e.g., an offset from) a timerelation formed between the GNSS system time, an RTD between time basesof at least two base stations and a time base of one of the two basestations.

At process block 906, the remote receiver 102A obtains satellitemeasurements from one or more of the satellites 110. These satellitemeasurements may, for example, be pseudoranges to a plurality ofsatellites. At process block 906, the remote receiver 102A may computeits position using the satellite measurements, and one or more of thetime offsets or time relations.

To facilitate the computing the position of the remote receiver 102A,the satellite measurements may be time stamped using clock circuitrysynchronized to the first time base because the remote receiver 102A isoperating in the first service area 112-1. Assuming that the time offsetand/or the time relation is formed as a function of the RTD, GNSS systemtime and the first time base, the time offset or time relation may beused to convert the time stamps so as to provide the precise GNSS systemtime.

Alternatively, the satellite measurements may be time stamped usingclock circuitry that has been adjusted to track the second time base.Assuming that the time offset and/or the time relations is formedrelative as a function of the RTD, GNSS system time and the first timebase, the time offset or time relation may be used to convert the timestamps to provide the time offset and/or time relation relative to thesatellite time. In turn, the first time offset may be used to obtain theprecise GNSS system time.

The position-determining process 900 beneficially allows the remotereceiver 102A to determine GNSS system time using the time offset and/orthe time relation. As above, if the remote receiver 102A is able toobtain air-interface timing for any of the cell sites (and notnecessarily a cell site serving the remote receiver 102A) it candetermine, using the corresponding time relations, the precise GNSSSsystem time.

Because the remote receiver 102A stores and/or maintains the timeoffsets and/or time relations and corresponding designations for lateruse with other cell sites, it can determine the precise satellite timewhen operating in any cell site for which it possesses a correspondingtime relation. This way, the remote receiver 102A can operateautonomously until it moves to a cell site for which it does not have acorresponding time offset or relation or unless one of the time offsetsor relations for a cell site becomes obsolete due to changes, updates orrevisions to the its air-interface timing. In such case, the remotereceiver 102A can perform the time-relation-forming process 400 (FIG.4), time-managing process 800 (FIG. 8) or other time relation formingprocess.

In the preceding discussion, the foregoing has been described withreference to application upon the GPS provided by the United StatesGovernment, which is just one example of a GNSS. It should be evident,however, that the foregoing is equally applicable to various otherGNSSs, and in particular, the Russian GLONASS system, the EuropeanGALILEO system; combinations of the GNSSs; and combinations of the GNSSsand other satellites, pseudolites, etc. that provide signals associatedwith, augmented for, derived from or otherwise modified for the GNSS,including, for example, the wide area augmentation system (WAAS) andSBAS. Accordingly, the term “GPS” used herein includes such alternativeGNSSs, including the Russian GLONASS system, the European GALILEOsystem, the WMS system, and the SBAS system, as well as combinationsthereof.

Variations of the apparatus and method described above are possiblewithout departing from the scope of the invention. For instance, in theexamples described above, controllers and other devices containingprocessors are noted. These devices may contain at least one CentralProcessing Unit (“CPU”) and a memory. In accordance with the practicesof persons skilled in the art of computer programming, reference to actsand symbolic representations of operations or instructions may beperformed by the various CPUs and memories. Such acts and operations orinstructions may be referred to as being “executed,” “computer executed”or “CPU executed.”

One of ordinary skill in the art will appreciate that the acts andsymbolically represented operations or instructions include themanipulation of electrical signals by the CPU. An electrical systemrepresents data bits that can cause a resulting transformation orreduction of the electrical signals and the maintenance of data bits atmemory locations in a memory system to thereby reconfigure or otherwisealter the CPU's operation, as well as other processing of signals. Thememory locations where data bits are maintained are physical locationsthat have particular electrical, magnetic, optical, or organicproperties corresponding to or representative of the data bits. Itshould be understood that the exemplary embodiments are not limited tothe above-mentioned platforms or CPUs and that other platforms and CPUsmay support the described methods.

The data bits may also be maintained on a computer readable mediumincluding magnetic disks, optical disks, and any other volatile (e.g.,Random Access Memory (“RAM”)) or non-volatile (e.g., Read-Only Memory(“ROM”)) mass storage system readable by the CPU. The computer readablemedium may include cooperating or interconnected computer readablemedium, which exist exclusively on the processing system or aredistributed among multiple interconnected processing systems that may belocal or remote to the processing system. It should be understood thatthe examples are not limited to the above-mentioned memories and thatother platforms and memories may support the described methods.

In view of the wide variety of embodiments that can be applied, itshould be understood that the illustrated examples are exemplary only,and should not be taken as limiting the scope of the following claims.Further, the claims should not be read as limited to the described orderor elements unless stated to that effect. In addition, use of the term“means” in any claim is intended to invoke 35 U.S.C. §112, ¶6, and anyclaim without the word “means” is not so intended.

1. A method comprising: obtaining, at a givenglobal-navigation-satellite-system receiver while being served by afirst node of a wireless network, a first time base, wherein the firsttime base is associated with the first node; obtaining, at the givenglobal-navigation-satellite-system receiver while being served by thefirst node, a relative-time difference, wherein the relative-timedifference comprises a difference between the first time base and asecond time base associated with a second node of the wireless network;obtaining at the given global-navigation-satellite-system receiver athird time base, wherein the third time base is associated with aconstellation of satellites; and forming a time relation as a functionof the first time base, the relative-time difference and the third timebase.
 2. The method of claim 1, further comprising: computing, asfunction of the time relation, at least one position of any of (i) thegiven global-navigation-satellite-system receiver, and (ii) a secondglobal-navigation-satellite-system receiver.
 3. The method of claim 2,further comprising: obtaining, at any of the givenglobal-navigation-satellite-system receiver and the secondglobal-navigation-satellite-system receiver from a database, the timerelation.
 4. The method of claim 1, further comprising: providing thetime relation to a database.
 5. The method of claim 1, furthercomprising: storing the time relation at the givenglobal-navigation-satellite-system receiver, wherein the givenglobal-navigation-satellite-system receiver is operable to compute, as afunction of the time relation, a position of the givenglobal-navigation-satellite-system receiver.
 6. The method of claim 1,wherein the third time base is an absolute time associated with theconstellation.
 7. The method of claim 1, further comprising: using thetime relation as an estimate of absolute time.
 8. The method of claim 1,further comprising: using the time relation to form an estimate ofabsolute time; and using the estimate of absolute time to increasesensitivity of the given global-navigation-satellite-system receiver. 9.The method of claim 1, further comprising: using the time relation toform an estimate of absolute time; and using the estimate of absolutetime to decrease a time for computing at least one position of any of(i) the given global-navigation-satellite-system receiver, and (ii) asecond global-navigation-satellite-system receiver.
 10. The method ofclaim 1, wherein forming the time relation comprises: applying the firsttime base to the relative-time difference to determine the second timebase; and forming the time relation as a function of the second andthird time bases.
 11. The method of claim 10, wherein forming the timerelation comprises: determining a difference between the second andthird time bases; and offsetting the difference from the third timebase.
 12. The method of claim 11, further comprising: computing, asfunction of the time relation, at least one position of any of (i) thegiven global-navigation-satellite-system receiver being served by thesecond node, and (ii) a second global-navigation-satellite-systemreceiver being served by the second node.
 13. The method of claim 1,further comprising: using the time relation to acquire at least onesatellite of the constellation of satellites.
 14. A method comprising:obtaining at a server a time relation, wherein the time relation isformed as a function of a first time base, a relative-time differenceand a third time base; wherein the first time base is obtained, at agiven global-navigation-satellite-system receiver while being served bya first node of a wireless network; wherein the first time base isassociated with the first node; wherein the relative time difference isobtained at the given global-navigation-satellite-system receiver whilebeing served by the first node; wherein the relative-time differencecomprises a difference between the first time base and a second timebase associated with a second node of the wireless network; wherein thethird time base is obtained at the givenglobal-navigation-satellite-system receiver; and wherein the third timebase is associated with a constellation of satellites; and providing thetime relation to any of (i) the given global-navigation-satellite-systemreceiver when being served by the second node, and (ii) a secondglobal-navigation-satellite-system receiver when being served by thesecond node.
 15. The method of claim 14, further comprising: computing,as function of the time relation, at least one position of any of (i)the given global-navigation-satellite-system receiver, and (ii) thesecond global-navigation-satellite-system receiver.
 16. The method ofclaim 14, further comprising: storing the time relation at the secondgobal-navigation-satellite-system receiver, wherein the secondglobal-navigation-satellite-system receiver is operable to compute, as afunction of the time relation, a position of the secondglobal-navigation-satellite-system receiver.
 17. The method of claim 14,wherein the third time base is an absolute time associated with theconstellation.
 18. The method of claim 14, further comprising: using thetime relation as an estimate of absolute time.
 19. Aglobal-navigation-satellite-system receiver comprising: memory adaptedto store executable instructions to: obtain a first time base whilebeing served by a first node of a wireless network, wherein the firsttime base is associated with the first node; obtain a relative-timedifference while being served by the first node, wherein therelative-time difference comprises a difference between the first timebase and a second time base associated with a second node of thewireless network; obtain a third time base, wherein the third time baseis associated with a constellation of satellites; and form a timerelation as a function of the first time base, the relative-timedifference and the third time base; and a processor adapted to (i)obtain from the memory the executable instructions, and (ii) execute theexecutable instructions.
 20. The receiver of claim 19, wherein theexecutable instructions further comprise: executable instructions tocompute, as function of the time relation, at least one position of thegiven global-navigation-satellite-system receiver.
 21. The receiver ofclaim 19, further comprising: a transmitter for providing the timerelation to a database.
 22. The receiver of claim 19, wherein the thirdtime base is an absolute time associated with the constellation.
 23. Thereceiver of claim 19, wherein the executable instructions furthercomprise: executable instructions to use the time relation as anestimate of absolute time.
 24. The receiver of claim 19, wherein theexecutable instructions to form the time relation comprise executableinstructions to: apply the first time base to the relative-timedifference to determine the second time base; and form the time relationas a function of the second and third time bases.
 25. The receiver ofclaim 19, wherein the executable instructions to form the time relationcomprise executable instructions to: determine a difference between thesecond and third time bases; and offset the difference from the thirdtime base.
 26. The receiver of claim 19, wherein the executableinstructions further comprise executable instructions to: use the timerelation to acquire at least one satellite of the constellation ofsatellites.
 27. A system comprising a firstglobal-navigation-satellite-system receiver, a secondglobal-navigation-satellite-system receiver, and a server, wherein: thefirst global-navigation-satellite-system receiver adapted to: obtain afirst time base while being served by a first node of a wirelessnetwork, wherein the first time base is associated with the first node;obtain a relative-time difference while being served by the first node,wherein the relative-time difference comprises a difference between thefirst time base and a second time base associated with a second node ofthe wireless network; obtain a third time base, wherein the third timebase is associated with a constellation of satellites; and form a timerelation as a function of the first time base, the relative-timedifference and the third time base; and the server is adapted to: obtainthe time relation from the first global-navigation-satellite-systemreceiver; and provide the time relation to any of (i) the firstglobal-navigation-satellite-system receiver, and (ii) the secondglobal-navigation-satellite-system receiver.